近日，日本东京工业大学的Y. Kondo及其研究小组取得一项新进展。经过不懈努力，他们首次观测到28O。相关研究成果已于2023年8月30日在国际权威学术期刊《自然》上发表。
该研究团队首次观测到了28O和27O，它们分别衰变为24O以及四个中子和三个中子。28O核特别引发兴趣，因为它是具有Z=8和N=20的幻数，在核结构的标准壳层模型图像中，预计它是相对少数的“双幻”核之一。同时，27O和28O都被发现存在狭窄的低共振，它们的衰变能量与复杂的理论模型结果进行了比较，包括大规模的壳模型计算和新开发的统计方法。在这两种情况下，潜在的核相互作用都是从量子色动力学的有效场论推导出来的。最后，研究结果表明，29F束产生28O的截面与不表现出封闭N=20壳结构的截面一致。
据悉，将物理系统置于极端条件下是一种常用的方法，可以更好地理解和更深入地了解其组织和结构。以原子核为例，研究人员通过研究与稳定原子核相比，中子与质子(N/Z)比值非常不同的同位素，来探索原子核的特性和结构。轻的、富含中子的同位素表现出最不对称的N/Z比，而那些超出束缚极限的同位素，经历自发中子发射，只以非常短的共振(约10-21秒)存在，为现代核结构理论提供了最严格的测试。
附：英文原文
Title: First observation of 28O
Author: Kondo, Y., Achouri, N. L., Falou, H. Al, Atar, L., Aumann, T., Baba, H., Boretzky, K., Caesar, C., Calvet, D., Chae, H., Chiga, N., Corsi, A., Delaunay, F., Delbart, A., Deshayes, Q., Dombrdi, Zs., Douma, C. A., Ekstrm, A., Elekes, Z., Forssn, C., Gapari, I., Gheller, J.-M., Gibelin, J., Gillibert, A., Hagen, G., Harakeh, M. N., Hirayama, A., Hoffman, C. R., Holl, M., Horvat, A., Horvth, ., Hwang, J. W., Isobe, T., Jiang, W. G., Kahlbow, J., Kalantar-Nayestanaki, N., Kawase, S., Kim, S., Kisamori, K., Kobayashi, T., Krper, D., Koyama, S., Kuti, I., Lapoux, V., Lindberg, S., Marqus, F. M., Masuoka, S., Mayer, J., Miki, K., Murakami, T., Najafi, M., Nakamura, T., Nakano, K., Nakatsuka, N., Nilsson, T., Obertelli, A., Ogata, K., de Oliveira Santos, F., Orr, N. A., Otsu, H., Otsuka, T., Ozaki, T., Panin, V., Papenbrock, T., Paschalis, S., Revel, A.
Issue&Volume: 2023-08-30
Abstract: Subjecting a physical system to extreme conditions is one of the means often used to obtain a better understanding and deeper insight into its organization and structure. In the case of the atomic nucleus, one such approach is to investigate isotopes that have very different neutron-to-proton (N/Z) ratios than in stable nuclei. Light, neutron-rich isotopes exhibit the most asymmetric N/Z ratios and those lying beyond the limits of binding, which undergo spontaneous neutron emission and exist only as very short-lived resonances (about 10-21s), provide the most stringent tests of modern nuclear-structure theories. Here we report on the first observation of 28O and 27O through their decay into 24O and four and three neutrons, respectively. The 28O nucleus is of particular interest as, with the Z=8 and N=20 magic numbers, it is expected in the standard shell-model picture of nuclear structure to be one of a relatively small number of so-called ‘doubly magic’ nuclei. Both 27O and 28O were found to exist as narrow, low-lying resonances and their decay energies are compared here to the results of sophisticated theoretical modelling, including a large-scale shell-model calculation and a newly developed statistical approach. In both cases, the underlying nuclear interactions were derived from effective field theories of quantum chromodynamics. Finally, it is shown that the cross-section for the production of 28O from a 29F beam is consistent with it not exhibiting a closed N=20 shell structure.
DOI: 10.1038/s41586-023-06352-6
Source: https://www.nature.com/articles/s41586-023-06352-6
来源：科学网 小柯机器人